Trunk piston



April 16, 12335. J, FLAMMANG EI' AL TRUNK PISTON Filed D80. 29, 1927 2 Sheets-Sheet 1 Jay/v April 16, 1935 Q .J. FLAMMANG EIAL TRUNK PISTON 7 Filed Dec. 29', 1927 2 Sheets-Sheet 2 Patented Apr. 16, 1935 umreo STATES PATENT ()FFlCE TRUNK PISTON Application December 29, 1927, Serial No. 243,268

20 Claims.

This invention pertains to pistons and more particularly to trunk pistons as used in internal combustion engines.

In the operation of an internal combustion engine, the weight of the piston plays an important part in determining the operation of the engine. This is because the piston must be accelerated to a high speed and then stopped and reversed in its direction of movement. These reversals take place in very rapid succession and cause considerable vibration. It has been proposed to overcome this difilculty by constructing .the piston of a light material so as to reduce its inertia to a minimum. The material most easily adapted to this purpose, on account of its lightness and cheapness, is aluminum or its alloys. These materials, however, have a high co-efficient of thermal expansion so that under operating conditions the piston will expand more rapidly than the cylinder within which it is expected to work. This causes diiliculty due to the liability of the piston binding in the cylinder on account of its expansion. If suflicient clearance is allowed between piston and cylinder to avoid binding, the piston becomes too loose for satisfactory operation when. the engine is cool. Various means for overcoming this difliculty have been proposed, such as making the piston in such form as to be resilient.

One of the objects of this invention is, therefore, to provide a piston, more particularly of light weight material, which in operation will maintain a substantially uniform bearing surface under the heat variances common to the normal operation of an internal combustion engine.

In casting a metal having a low co-efflcient of thermal expansion integral with a metal having a high co-efllcient of expansion, difilculties arise by reason of the fact that the metals grip each other, so that one 'or both of the metals are stretched or compressed, as'the case may be, and thus defeat the purpose sought to be obtained.

Another object of this invention is, therefore,

to provide a method of casting a piston having a bearing element with a low co-eflicient of thermal expansion integral with a body of different metal having a high co-eflicient of expansion, in such a manner that one metal will not grip the other and thus affect their normal expansion under heat.

Further objects will appear from the detailed description taken in connection with the accom panying drawings, in which- Figure 1 is a cross section of a trunk piston embodying this invention, taken on a line 90 degrees from the center line of the wrist pin;

Figure 2 is a cross section taken on line 22, Figure l; 1

Figure 3 is a cross section taken on line 3-3,

Figure 1;

Figure 4 is a view similar to Figure 2, showing another embodiment of this invention;

Figure 5 is a view similar to Figure 3, showing 10 another embodiment of this invention;

Figure 6 is an enlarged view of a part of the piston;

Figure 7 is a view similar to Figure 1, showing another embodiment of this invention;

Figure 8 is a cross section taken on line 8-4, Figure 7.

Figure 9 is a cross sectional view similar to Figure 2 and showing another-embodiment.

Figure 10 is a cross sectional view similar to 20 Figure 4 and showing another embodiment.

Referring to the drawings, I designates the body of the piston which is in this case of the trunk type. The piston comprises a head 2, having a skirt 3 provided with the usual wrist pin 25 bosses 4. The body portion of the piston may be constructed of aluminum, or one of its alloys, or of some other suitable material preferably of light weight but of high thermal expansion. Inserted in the piston is an abutment or plate 5 30 placed diametrically across the piston, perpendicular to the vertical plane of the wrist pin, its outer edges terminating in one of the ring grooves 6, and anchored at its center by a pin II. This plate is made of a substantially non-expansible 35 metal; by substantially non-expansible metal" as used here, is meant a metal which has a coeflicient of thermal expansion which is small as compared with that of the body of the piston.

A metal suitable for this purpose is invar" steel,

which is practically without any appreciable increase in size with increase in temperature. In the embodiment illustrated in Figure 1, there are two such plates. The plate l5, at the bottom, must be of somewhat different shape to permit the connecting rod to pass therethrough and oscillate therein. Such a plate is, therefore, provided with a space 1.

The packing rings 8 are preferably formed so as to be of uniform thickness throughout their circumference and are dimensioned so that when seated in the groove against the plates 5 and I5, they will fit the cylinder in such a manner as to provide a firm bearing for the piston against the cylinder wall. The ends of the abutments I and l5 project beyond the bottom of the ring groove, while the ring groove is wider than the abutment so that the groove will be undercut with respect to the abutment, as shown in Figure 6. The outer edges of the abutments are machined to an arc of a circle and so proportioned that the rings 8 will have the proper sliding fit on the cylinder wall while these rings bear abutments. The rings 8, therefore, provide a firm bearing to support the side thrust of the connecting rod during the operation of the engine. The rings 8 may be constructed of cast iron or another material suitable for piston rings. They are usually split as is preferable in packing rings so as to be resilient circumferentially. This provides that the rings 8 will always exert a yielding pressure on'the cylinder walls and so they will expand as wear takes place. Additional packing rings 9 fitted in piston ring grooves of the usual type may also be provided for additional packing between the combustion chamber and the crank case and each of the grooves may be provided with a bearing plate as described, although this is not necessary. Inside the piston at its top and at its center is provided a projection IIJ against which the top of abutment 5 may rest and to which it may' be anchored by a pin ll.

An abutment plate 25, cross shaped, as shown in Figure 4, may be used in place of the plate 5. In using the plate 25, one of the cross pieces is placed parallel with the wrist pin. Similarly a. plate 35, Figure 5, may be employed in place of plate 15.

Referring to Figures 7 and 8, parallel abutment plates 45 may be positioned to form chords instead of diametrically as shown in previous figures. Bosses l2 may be cast integral with the piston on the thrust side thereof, and pins ll inserted therethrough and through the plates to form an anchorage. The diametrically arranged abutments may be secured in a similar manner.

Figures 9 and 10 illustrate embodiments wherein the diametrically arranged abutments 5 and 25,

corresponding respectively to Figures 2 and 4, are secured at one end to the metal of the piston by pins II retained in bosses [2 on the interior of the piston.

During the operation of the engine the piston heats and expands, but the abutments maintain their original size or substantially so, and will thereby limit expansion of the piston ring bear-' ing at the point where the packing ring is applied. The piston skirt itself is machined to such a diameter, even at the ring lands, as to have ample clearance in the cylinder so that under no conditions of expansion will it be liable to contact with the cylinder wall or to bind therein, since the abutments maintain their diameter substantially constant. The packing rings 8, which are seated thereon and surround the same, will, therefore, maintain a substantially constant bearing on the cylinder wall. It will, of

course, be understood that the abutments are machined to proper diameter; this diameter is such that when a packing ring 8 is in place so as to bear against the abutment, the opposite diameters of the piston rings as seated will correspond to the diameter of the cylinder. These packing rings will, however, project beyond the piston body so as to keep the same out of contact with the cylinder even when maximum expansion takes place; accordingly, the packing rings provide a bearing surface as well as sealing means. The body of the piston may be cast of such light weight material as described, suitable slots cut in the periphery thereof by milling and breaching, or otherwise to accommodate the abutments, which are then inserted and fastened, as described.

It will be observed that an abutment of the form 25, 35 cannot be inserted as above described; however, they may be inserted in the mold and thus cast integrally with the piston. It is essential, however, that in casting, the two metals do not come intosuch close contact as to grip each other. In such event, the metals will stretch or become compressed, thus having a common thermal expansion and defeat the purpose of the abutments. The plates are, therefore, coated with a refractory, friable material before being placed in the mold. A silica enamel, calcined on the plates is suitable for this purpose. After so coating, the plates may be placed in the mold and body of the piston cast around them, the enamel being undisturbed. In the alternate heating and cooling of the piston, the enamel will not sustain the stresses set up and will readily crack so that either the plates or the body of the piston may contract and expand without affecting the other. After casting, the plates may be anchored by either of the methods heretofore described. Pinning or otherwise fastening the plates 25, 35 is, however, largely unnecessary, since the cross bars serve to securely hold the plates centrally with reference to the body. The extended edges of the abutments are machined to accurate dimensions, preferably after the piston is cast.

It will be seen that this invention provides a piston which may be cast of light metal irrespective of the degree of expansion which such metal may undergo upon heating. This is due to the fact that the bearing surfaces are formed by the packing rings seated against the abutment plates which are anchored to the body of the piston. The rings 8 may perform functions of both piston rings and bearing rings. The construction is such that the expense of manu ,facturing the piston is not materially increased.

The abutment plates are themselves of simple and cheap construction.

While the invention is particularly applicable to trunk pistons for internal combustion engines, it is obvious that many of these features are capable of use in other pistons, etc. Furthermore, while the abutments 5, I5, 25 and 35 are preferably of a practically non-expansible ma-v terial, such as invar steel, it is feasible to use ordinary steel and still attain some of the objects of this invention; for steel has a low co-eflicient of expansion compared to aluminum and is, therefore, substantially non-expansible in a comparative sense. Furthermore, since the cylinder is usually of cast iron and subject to expansion, even a steel abutment will merely follow the cylinder as the temperature of both increases. It is, therefore, to be understood that the expression substantially non-expansible is to be construed accordingly. It will also be seen that it is not absolutely essential that an abutment be placed at the skirt end of the piston, for this skirt may be formed in the usual manner and split so as to provide for resiliency, and still obtain some of the'objects of this invention. It will, therefore, be understood that certain features, operations and sub-combinations are of utility and maybe employed without reference to other features, operations and sub-combinations. That is contemplated and is within the scope of the appended claims. It is further obvious that various changes may be made in details, within the scope of the appended claims, without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

Having thus described the invention, what is claimed is:

l. A trunk piston of high thermal expansion having a ring groove, a ring in said groove, and substantially non-expansible abutments for said ring, said abutments extending in parallel chordal relation across the piston and tenninating in said groove.

2. A trunk piston of high thermal expansion having a head and skirt each provided with a groove, a packing ring in each of said grooves, anda plurality of non-expansible abutments extending in chordal relation to said rings for sustaining the latter free of the groove bottoms.

3. A trunk piston of high thermal expansion having a head and skirt each provided with a groove, a packing ring in each of said grooves, a plurality of non-expansible abutments extending in chordal relation to said rings for sustaining the latter free of the groove bottoms, and means at one end of said abutments for securing the same to the wall of the piston, the

opposite ends thereof being movable through' the wall of the piston during expansion of the latter.

4. A hollow piston having an external ring groove and an opening through the wall of the piston to the bottom of said groove, a bearing ring in said groove, and a strut extending entirely across the piston and through said opening into said groove and engaging the inner surface of said ring.

5. A hollow piston having a ring groove and an opening through the wall of said piston to the bottom of said groove, a bearing ring in said groove, and a strut extending entirely across said piston, the said strut having one portion thereof secured to said piston, and another portion thereof extending through said opening and engaging the inner surface of said ring.

6. A hollow piston having an external ring groove and an opening through the wall of the piston to the bottom of said groove, a bearing ring in said groove, and a strut extending across said piston and through said opening engaging the inner surface of said ring, said strut being freely laterally expansible.

7. A hollow piston having an external ring groove and diametric openings through the walls of said piston to the bottom of said groove, a ring insaid groove, and a strut extending across said piston, the ends of said strut extending,

through said openings and contacting said ring.

8. A hollow piston having an external ring groove and slots arranged diametrically of the piston, the said slots opening into said groove, a strut extending transversely of the piston and having the ends thereof positioned in said slots, the said strut being attached intermediate the ends thereof to said piston.

9. A hollow piston of high thermal expansion having a ring groove and an opening through the wall of said piston to the bottom of said groove, a bearing ring in said groove, and a relatively inexpansible strut extending entirely across said piston, the said strut having one portion thereof secured to said piston, and another portion thereof extending through said opening and engaging the inner surface of said ring.

10. A hollow piston of high thermal expansion having a ring groove and an opening through the wall of said piston to the bottom of said groove, a bearing ring in said groove, and a relatively inexpansible strut positively anchored to the body of said piston at a substantial distance from said opening, a portion of said strut extending through said opening and engaging the inner surface of said ring.

11. A hollow piston having an external ring groove and an. opening through the wall of the piston to the bottom of said groove, a bearing ring in said groove, and a strut within the piston afiixed at one end to the body of the piston and having its opposite end extending through said opening into said groove to engage the-interior of said ring at a single point.

12. A hollow piston having an external ring groove and an opening through the wall of the piston to the bottom of said groove, a bearing ring in said groove, and a strut within the piston aflixed at one end to the body of the piston and having its opposite end extending through said opening into said groove to engage the interior of said ring at a single point, said strut having a coefficient of expansion less than that of the cylinder.

13. A hollow piston having an external ring groove and an opening through the wall of the piston to the bottom of said groove, a bearing ring in said groove, and a strut within the piston afiixed at one end to the body of the piston and having its opposite end extending through said opening into said groove to engage the interior of said ring at a single point, said strut having a coefficient of expansion lower than that of the piston.

14. A piston for internal combustion engines having an external ring groove, an expansible bearing ring mounted inv said groove, and a thermally responsive element having one end rigidly secured to an inner Wall of said piston and having its other end in engagement with the interior of said ring at a single point in its circumference to limit the movement of said ring into the groove at said point.

15. A piston for internal combustion engine cylinders, having an external ring groove in the body thereof, an expansible bearing ring mounted in said groove, and a thermally responsive element having one end in engagement with the interior of said ring at a single point in its circumference to limit the movement of the ring into the groove at said point whereby to maintain the diametrically opposite side of the piston body in constant contact with the walls of the engine cylinder.

16. In an aluminum alloy piston, a diametrically extending strut of a material having a lower co-eificient of expansion than the aluminum alloy, one end of the strut being secured to the metal of the piston and the other extensible into one of the piston ring grooves.

17. A piston for internal combustion engines having a head provided with a ring groove, a circumferentially elongated slot in the bottom of said groove extending through the piston wall, a fiat thermally responsive strut extending diametrically across said head and having one end slidably fitting in said slot and its opposite end rigidly secured to the interior of the piston wall at a point diametrically opposite said slot, and

an expansible bearing ring mounted in said groove, said first mentioned end of said strut engaging the interior of said ring at a single point in its circumference to limit the movement of the ring into the groove at said point.

18. A hollow piston having a ring groove and an opening through the wall of said piston to the bottom of said groove, a bearing ring in said groove, and a strut extending entirely across the interior of said piston, the said strut having one portion thereof secured to said piston, and another portion thereof extending through said opening and engaging the inner surface of said ring.

19. A hollow piston having a ring groove and an opening through the wall of said piston to the bottom of said groove, a bearing ring in said groove, and a strut extending across said piston,

the said strut having one end thereof secured to the piston, and the other end thereof extending through said opening and engaging the inner surface of said ring.

20. A hollow piston having a head provided with an external ring groove, a circumferentially elongated slot in the bottom of said groove extending through the wall of the piston, a strut in-the form of a flat metal strip extending diametrically across the piston and having one end slidably fitting in said slot and contacting with the metal of the piston wall adjacent its opposite end, at a point diametrically opposite the slot.

- JOHN FLAMMANG.

PERCY L. BOWSER. 

